That doesn't contradict his statement. Just that starting Chess specifically from an early age with a lot of instruction will make you very good at Chess. That

That doesn't contradict his statement. Just that starting Chess specifically from an early age with a lot of instruction will make you very good at Chess. That doesn't mean anything about their intelligence level. E.g. almost every famous athlete has been practicing their craft from a young ago, some of them pushed to practice much more than their peers. Some of them are then successful. I wouldn't call any of it proof of their adult intelligence, just skilled at gymnastics/tennis/swimming/whatever.